The present invention relates to a surface-analysis technique in general and to an X-ray analysis method and apparatus of residue on the surface of a specimen or a sample in particular.
In order to promote the large-scale integration of semiconductor devices, it is necessary to establish a fine-line patterning process technology at a level smaller than the deep submicron. In the manufacturing of 1-Gb DRAMs (Dynamic Random-Access Memories) , for example, a patterning process of a contact hole having a diameter of 0.16 .mu.m and a depth of 2 .mu.m is required. In order to establish such a fine-line patterning process, technologies of analysis for measuring and inspecting the accuracy of the fine-line patterning are necessary. In particular, technologies of analysis that can be used for analyzing the composition and thickness of residue are required. In this residue analysis, points to be taken into consideration are the fact that the surface of the sample (wafer) is not necessarily flat so that areas having large steps such as a small contact hole described earlier also need to be analyzed as well.
The conventional residue analysis for analyzing areas having large steps is carried out by destructing a fabricated wafer and observing the cross section of the destructed wafer by means of an SEM (Scanning Electron Microscope). With this technique, however, the composition of the residue cannot be identified only by observation of the shape and, on top of that, the wafer cannot be returned to the manufacturing process after the analysis once the wafer has been destructed. Other problems with this technique include the fact that it is difficult to observe a trace of residue of the order of few nm. In the development of semiconductor integrated-circuit devices after Gb, the above problems which entail deterioration of the yield and the precision of analysis are regarded as fatal problems.
On the other hand, an X-ray analysis method, which is an analysis technique allowing analyses to be done without destructing a wafer, is available. An example of a typical X-ray analysis method is the use of charged-particle analysis equipment disclosed in Japanese Patent Laid-open No. Sho 63-243855. With this charged-particle analysis equipment, an irradiated electron beam is applied to the surface of a sample. An X-ray generated from the surface of the sample due to the application of the irradiated electron beam thereto is then observed. The X ray is observed by means of a light splitting crystal placed at an angle of about 22 degrees from the center axis of the electron beam.
In order to carry out qualitative and quantitative analyses on residue by using X-rays, the place at which a means for observing the X-rays is installed is important. Specifically, in order to prevent the X-rays generated by the surface of the sample from being absorbed by an obstacle, the means for observing the X-ray must be placed at a location where no such obstacle exists. Unfortunately, however, there has been so far no clear standard concerning the location for installing a means for observing the X-rays and no much attention has hence been paid to such an installation position. In the case of the charged-particle analysis equipment mentioned above, a light splitting crystal is positioned at an angle of 22 degrees. None the less, the absorption of the X-rays cannot be avoided in some cases. In particular, in the case of large-scale integrated memories beyond the 4-Mb DRAM which are considered to be the main semiconductor devices in the future, by merely using the charged-particle analysis equipment, it will be impossible to perform qualitative and quantitative analyses of residue on the surface of a sample.